With accent marks:
Кто о чём, а вши́вый о ба́не.
Who is talking about what, and a lousy one about the bath.
This saying describes a situation when in a conversation of several people, one of them always talks only about what worries him. Even if the discussion is about a completely different thing. In the saying, such a person is compared to a "lousy one talking about the bath". Because until he bathes, and until this does not ease his suffering from the lice biting him, he will not care about anything else.
You can use this saying when someone always falls back on talking about the same thing.
Other Russian proverbs
Get your sleigh ready in summer and your (horse-drawn) cart in winter.
The demon is not as scary as he is depicted.
Some to the forest, some for firewood.
A bad example is contagious.
Forewarned is forearmed.
~ Seven babysitters make the kid to lose an eye.
We got what we fought for.
Don’t wave your fists after the fight.